XWIKI-14730: Using $displayDocExtra false hides tags and document footer information (creator and creation date)
- Since $displayDocExtra is now working without side-effects, replaced usages of $docextras in our code.

* Remove the white space at the start of the administration sections (in order to be aligned with the menu).
* Improve the styles.
* Add more hints (for registration and invitation sections).
* Fix the Extension Updater and History section (the help text from the start of the section should be displayed only on view action).

* Small improvements to the Users & Rights sections.

* Improve the sections from the Other category.
* Move Invitation and User Directory sections to the Users & Rights category
* Move Application Panel section to the Look & Feel

* Fix deprecated usages in WebPreferences.xml pages

* not saving each email invitation token separately seems to fix this issue
* update save comment to reflect the fact it might have saved one or several invitations

XWIKI-13325: Invitation app removes hyphens in domain name and replaces them with strikethrough formatting

- replace unnecessary xml escape by necessary xwiki escape